378 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1937 



two species readily distinguished by structural differences. Later 

 studies showed that their newly described americana is the primary 

 pest, the one which feeds on Uving tissue. This, although complicating 

 the whole screwworm problem in a certain sense, simplified it in other 

 ways and demonstrated again the value of taxonomic studies. Such 

 studies make it possible to differentiate control measures in the field, 

 to dispose properly of infested shipments moving in commerce, and to 

 apply ai)propriate quarantine measures. 



Life-history studies and studies in the laboratory and in the field to 

 find out how the insect fives, how it propagates, how it feeds, how it 

 damages or benefits crops or food or materials, teach us not only about 

 the insect but also what to do about it, a large part of the program of 

 treating of insects. After several years of experiments in the effort to 

 control wireworms, the immature form of the click beetle, physiologi- 

 cal studies in connection with the fife-history studies developed that 

 the particular poisons being used were not being taken into the 

 system by the insect but were being thrown out before reaching the 

 stomach. 



Spraying with lead arsenate has long been a standard form of 

 control of insects that bite and chew. Until the human health 

 hazard involved in the use of lead arsenate was fuUy realized, it was 

 the accepted standard method of control for codling moth, that almost 

 universal pest of apples and pears. Studies on the life liistory and 

 habits of the Oriental fruit moth made shortly after its discover}^ in 

 this country revealed that the larva, although a biting and chevidng 

 form somewhat similar to that of the codling moth, has a habit of 

 spitting out the first one or two mouthfuls of food and thus escapes 

 the effects of the poison sprayed on the surface of the fruit or twig; 

 hence in this case lead arsenate is not effective. 



As is well known, the fecundity of insects is remarkable. Taking the 

 classic example of the ordinary vinegar fly as computed by Maxwell- 

 Lefroy — if the offspring of a single pair lived for 1 year and none of 

 the yomig died and none of the bodies decomposed, the total mass of 

 ponderable material produced would bury the entire earth a million 

 miles deep. Of course, there is nothing to worry about in this direc- 

 tion, because it never would happen. In the first place, comparatively 

 speaking, almost aU the offspring die and those that die do decay, so 

 there is no ponderable mass of suflBcient size left to bury any 

 part of the earth. Despite the fact that such a large proportion of the 

 offspring of insects do die, however, there is a tremendous increase in 

 the population of destructive insects from year to year. Notwith- 

 standing these tremendous populations of insect pests from time to 

 time which take a huge toll in crops and which spread disease and 

 annoy human kind in other ways, there is no such thing as the insects 

 of the world wiping out civilization. However, if crops and foods are 



